1. Field of the Invention
This invention relates to a signal processing system which is best suited for a sound source for use in an electronic musical instrument or a voice synthesizing device and the like.
2. Description of the Prior Art
According to the prior art sound source device for use in an electronic musical instrument or a voice synthesizing device and the like, a vibratory wave form signal from a mechanical sound producing body or an electrical oscillator is derived as a music signal directly or via a demultiplier or a filter circuit, or a signal wave form or an envelope wave form and the like of a music signal are stored in a memory means, and then the contents thus stored are read out digitally, thereby reproducing a music signal.
For instance, in the case of an electronic musical instrument equipped with an oscillator, a filtering characteristic of a filter circuit is controlled, or two or more oscillating signals are synthesized, thereby deriving a given wave form or spectrum, and in addition, the music signal thus derived is envelope-controlled, thereby obtaining a percussion tone.
Meanwhile, it is difficult to derive a music signal such as are produced by a piano, whose higher harmonic frequency is not an integer-multiplication of a basic frequency and yet spectral construction varies with the time.
For instance, with a music synthesizer equipped with a voltage control type filter, it is possible to vary, relative to the time, the spectral construction of a music signal which may be derived by controlling the filter characteristic relative to the time. However, a massive construction is required for an apparatus for playing a complex sound such as those of a piano. Hitherto, there is known an electronic musical instrument, as a sound source device equipped with memory means, wherein actual music is stored in a magnetic tape or an optical disc and the like, and then music signals stored in response to the operation of keys in a keyboard are read out and reproduced. Such a prior art musical instrument is complicated in construction, and has to be subjected to a time limitation imposed on the music obtained, thus failing to accommodate itself to speedy play or play wherein one sound is continued for a long duration, or to obtain a music signal whose spectral structure is varied relative to the time.